Armillaria root rot is a major disease affecting Japanese larch and the hybrid larch Larix gmelinii var. japonica×Larix kaempferi, F₁, which are representative plantation tree species in Hokkaido, Japan. Assessing the disease risk is crucial for the successful cultivation of F₁ seedlings. Armillaria root rot damages are also associated with tree species and host tree declines. Responses to environmental factors, such as moisture conditions, vary between Japanese larch and F₁, leading to the hypothesis that the local topography susceptible to Armillaria root rot differ by the two species. In this study, we specifically tested this hypothesis by examining the local topography in a mixed plantation of both species. We evaluated the disease status in a total of 1,318 trees (Japanese larch or F₁ hybrids) along with local topographical conditions from 2021 to 2023. The results showed a significantly higher incidence of Armillaria root rot in the F₁ (22.3％) than in Japanese larch (8.3％) up to six-year-old, with new damage occurring around previously affected trees. The relationship between Armillaria damage and local topography showed opposite trends among the species; Japanese larch was estimated to be more susceptible in moist areas, and F₁ was estimated to be more susceptible in dry areas. The model indicated that F₁ is generally more susceptible to Armillaria root rot, but Japanese larch is more vulnerable in wet conditions. These findings suggest that it is essential to consider the impact of local topography on the management of Armillaria root rot in larch species.

We investigated the growth of sugi (Cryptomeria japonica D. Don) saplings during 6 years after planting and branch increments during the last two years under different competing vegetations (Miscanthus sinensis-dominated and deciduous tree-dominated) in order to clarify the effects of vegetation changes derived by continuing or omitting the weeding practices on the growth of planted sugi saplings. Miscanthus increased their dominance from the fourth year by continuing weeding, while the vegetation changed toward non-Miscanthus-dominated (deciduous tree-dominated) type one or two years after omitting weeding. The sugi planted in the initially deciduous tree-dominated site gained great advantages in vertical competition against the competing vegetation. Although sugi planted in the initially Miscanthus-dominated site gained advantages after continuing weeding for 3 to 4 years, their growth continued to be suppressed even after achieving the height advantages and/or after the vegetation change to non-Miscanthus type: the suppression was especially apparent in diameter growth. The branch increment of planted sugi during the same period was also less in the initially Miscanthus-dominated site compared to the initially deciduous tree-dominated site even at the parts higher than competing vegetation. We concluded that the suppressed crown development surrounded by thick Miscanthus cover at the early stage (ca. four years) resulted in the continuous restriction of further growth after changing the vegetation types and competition status, suggesting that weeding omission should be avoided in a Miscanthus-dominated vegetation.

To consider the future of using forest biomass for bioenergy, 81 papers published since 2012 on woody biomass power generation in Japan were reviewed. The focus was placed on three issues: fuel supply, greenhouse gas (GHG) emissions and emission reductions, and regional impacts. An analysis was carried out on 36 papers examining at least one of these topics. In the context of fuel supply, various themes were examined, such as the impact on supply chains, availability, and procurement costs. It was found that the supply of conventional wood materials and the demand for fuelwood are interrelated. The methods and results for calculating GHG emissions and reductions differed, based on how emissions during combustion were treated. This indicates a need for clarification in the debate on the carbon neutrality of woody biomass and the conditions required for achieving carbon neutrality. With respect to regional impacts, while the local community's acceptance of woody biomass use was noted, no studies focused on resilience when exploring the secondary effects. Consequently, a comprehensive analysis of woody biomass use, considering regional characteristics, is desirable. Although the use of woody biomass has the potential to contribute to a sustainable society, it may also have adverse effects. It is, therefore, necessary to explore its use and the associated supply chains from multiple perspectives.